What Is Flow Cytometry?

A laboratory technique used to identify and count cells

Flow cytometry is a lab technique used to look at individual cells in a sample of blood, semen, or bone marrow. Flow cytometry results can be used for cancer diagnosis and treatment, to monitor the health of people with HIV, and other purposes.

Flow cytometry is helpful when a health professional needs to look at a large number of cells, one cell at a time. These cells are sent through a very narrow tube, allowing the properties of individual cells to be measured using lasers or other types of light.

This article discusses how a flow cytometry test works and when it is used. It will also help you to know more about how a flow cytometry analysis is done, what to expect, and what the results typically mean.

CD3/CD4 test
jarun011 / Getty Images

What Flow Cytometry Is Used For

Flow cytometry is used in many areas of clinical testing. That's because flow cytometry analysis provides a relatively straightforward way to look at specific types of cells, including:

  • Cancer cells
  • Immune cells
  • Sperm cells

As long as there is a way to mark cells for detection, this method can be used to find them. Usually, all it takes to identify a specific type of cell is to create a monoclonal antibody to recognize that cell. Then a fluorescent dye is attached to the antibody. Flow cytometry can find all the cells that the antibody targets.

There are a number of common uses for flow cytometry:

Immune Function With HIV Infection

Flow cytometry analysis is used to count the number of CD4 T-cells in the blood of someone with HIV. This helps to determine how healthy their immune system is and to track any damage caused by the virus. This is generally done on a blood sample.

Bone Marrow and Anemia

The flow cytometry test is used to count the number of reticulocytes (immature red blood cells) in the bone marrow. This can help to determine the cause of anemia. It can also be used to check the health of the bone marrow after a transplant or after chemotherapy. This is generally done on a bone marrow sample.

Organ Transplants

Histocompatibility (HLA) testing is done prior to an organ transplant, whether someone is intended to be a donor or a recipient. This is generally done on a blood sample using flow cytometry analysis.

Sperm Counts

Flow cytometry is used to check the number of sperm in a semen sample. This may be done either as part of an infertility workup or to see if a vasectomy has been successful.

Blood-Related Cancers

Flow cytometry results can be used to diagnose and classify leukemia or lymphoma. This may require a blood sample, bone marrow, or a different type of tissue sample.

Blood Clotting Disorders

Flow cytometry analysis is done to assess whether your platelets, blood cells that are a key part of your clotting system, are working correctly.

The specific flow cytometry test and type of sample will depend on the information a healthcare provider needs. The same thing is true for any other tests ordered, such as histochemistry when diagnosing certain types of cancer.

How Flow Cytometry Works

Flow cytometry is based on isolating the individual cells in a sample that contains many cells. The test allows healthcare providers to look at specific cells one at a time. This is accomplished by processing cells through a common flow cytometry protocol.

The flow cytometry results are then used to diagnose or monitor a specific health condition. While these tests are useful in a variety of situations, they have limitations.

For example, the presence of inflammation can alter the numbers of specific types of blood cells in a sample. This can lead to a false negative or false-positive test result for certain types of cancer.

With semen analysis, recent sexual activity can make the test inaccurate. Platelet function test results can be affected when taking a non-steroidal anti-inflammatory drug (NSAID).

How Accurate Is Flow Cytometry?

How accurate flow cytometry will be depends on a number of factors, including the type of test done, the quality of the samples, the skill level of the pathologist, and the equipment used both for taking the samples and analyzing them.

Some of this equipment may include:

  • IV or other needles, as well as specimen collection tubes for samples
  • Imaging to guide the biopsy or other flow cytometry sampling procedure
  • Special machines designed for laser processing of the sample
  • Advanced computers to guide procedures and to process results
  • Automated systems increasingly used in flow cytometry data

Risks and Contraindications

The risks associated with flow cytometry are limited to the risks associated with sample collection, and will depend on the type of sample needed.

A blood sample or semen sample presents comparatively low risk when collected. In contrast, a bone marrow sample or tissue sample is more difficult, and carries some additional risks.

These tests are still considered to be quite safe. The risks of bone marrow aspiration and/or tissue biopsy are uncommon but may include:

  • Bruising at the site
  • Bleeding from the site
  • Infection
  • Reactions to anesthesia

Your healthcare provider may start with flow cytometry on a blood sample before moving on to more invasive testing. There are no specific contraindications to flow cytometry, although a flow cytometry protocol may need to be adapted for some people.

What to Expect

If you will be having a test involving flow cytometry, there are some general steps that you can expect. Talk to your healthcare provider, however, about your specific situation.

Before the Test

Preparation for a flow cytometry test depends on its purpose and your individual medical history. In some cases, a sample can be taken at the time your healthcare provider determines a need for it. In others, you may need to return after stopping certain activities or medications that you take.

You should also let your healthcare provider know if you're pregnant or think you might be pregnant, and if you're sensitive or allergic to any medicines or medical items, such as latex.

If your healthcare provider wants you to have a flow cytometry test, it's important to ask how any medications or supplements you take might affect the test results.

A blood sample taken for flow cytometry is done the same way as other blood draws, and should only take a few minutes. A semen sample would be expected to take longer, and bone marrow samples will be more complicated samples to take, depending on the sedation you'll need for it. In all cases, it will depend on the type of sample.

The amount of time it takes to get a sample for flow cytometry tests will depend on the type of tissue. Getting a sample from the liver is very different from getting a sample from a lymph node.

Some samples can be taken at your healthcare provider's office but others will need to be done at an outpatient surgical center. If you are undergoing a bone marrow test or other biopsy, you may need to remove clothing and jewelry prior to the test. A hospital gown will be provided.

You should be able to eat and drink as usual before a flow cytometry test, but that may change if certain types of sedation are required. Check with your healthcare provider for recommendations.

Is Flow Cytometry Expensive?

Flow cytometry can be expensive and some insurers require prior authorization before these tests are done. Check with your insurance company and provider about any requirements. Remember to bring your health insurance card and photo identification to your appointment too.

During the Test

You may see a range of healthcare providers, depending on the type of sample needed for your flow cytometry test. The healthcare team members will play different roles during your appointment.

For example, a technician takes the blood sample during a fairly simple procedure. For a bone marrow aspiration and biopsy, you may see a healthcare team that includes other specialists.

Bone marrow tests and many biopsy procedures will require a small incision at the site, and the insertion of a needle while you remain still. Imaging may be used to guide the process.

A healthcare provider will place pressure on the site to control any bleeding after the sample is taken, and cover the site with a bandage. You will then be asked to lie still for 10 to 15 minutes. If you experience any pain or discomfort after your test, you may be told to take a pain reliever.

In some cases, your healthcare provider may follow up to evaluate your recovery after the samples needed for a flow cytometry test.

After the Test

In most cases, you don't need to change your routine after a blood draw needed for flow cytometry analysis. For bone marrow and biopsy samples, you may need to limit activity or avoid bathing for 24 hours or more. Your healthcare provider will offer specific instructions to follow after the test.

It is important to contact your healthcare provider if you experience any of the following after a bone marrow test or other biopsy:

  • Fever
  • Bleeding that doesn't stop or that soaks through the bandage
  • Pain that gets worse with time
  • Swelling at the site of the biopsy
  • Redness or drainage at the biopsy site that gets worse with time.

If you have mild to moderate pain after one of these procedures, it should generally be manageable with over-the-counter pain medications. However, if you have any bleeding issues, you may be instructed not to use aspirin and certain other products. Check with your healthcare provider about what pain medications would be best.

Interpreting Results

A flow cytometry analysis can take up to several weeks to come back. This will depend on the specific types of cells under investigation, as well as what lab is used. Flow cytometry is a very technical test, and many labs may have only limited ability to process samples.

There are several common types of flow cytometry test results.


This flow cytometry test is used to diagnose leukemia or lymphoma. This test is usually done after atypical results are seen on a complete blood count or white blood cell (WBC) differential. These results will explain if any abnormal cells are present and what types of cells they are, as a part of your diagnosis.

Reticulocyte count

This test evaluates bone marrow function and red blood cell production. It is usually interpreted in combination with other test results, such as red blood cell count and/or hematocrit. The results of this test should not be interpreted on its own. Both low and high values can be fine, or problematic, depending on the circumstances.

CD4 counts

The flow cytometry analysis gives the number of CD4 cells in a cubic millimeter of blood. A normal CD4 count is between 500 and 1500. If your CD4 count is below 500, it means that your immune system may be suppressed. Causes may include HIV or drugs used to suppress your immune system. For people with HIV, CD4 counts can vary with time even without your health changing.

Your healthcare provider will probably tell you about patterns in your test results, rather than looking at specific results. For people on immunosuppression drugs after an organ transplant, a low CD4 count means those drugs are working.

HLA test results

These test results will say whether or not an organ donor and recipient are matched and, if not, how many mismatches they have. Low numbers mean that a transplant is more likely to be successful, and a pairing with no mismatches is best.

Semen analysis

These flow cytometry test results are used to report how many sperm are in a sample as well as how well they are functioning.

If flow cytometry is used for diagnosis, it will only be done once. However, if flow cytometry is being used to monitor a health condition, you may need to have the test repeated on a regular basis.

For example, people with HIV may be recommended to undergo CD4 testing as often as every six months, or even more frequently, depending on how they are responding to medication.

A Word From Verywell

Talk to your healthcare provider about what to expect. That means asking not just how quickly you'll be likely to receive your results but what, if any, additional testing may be needed. It's possible that flow cytometry may be just the first step in understanding your health condition. You also may wish to consider support from people living with cancer, HIV, or a similar diagnosis to your own.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Yale School of Medicine. Yale flow cytometry.

  2. Pophali PA, Timm MM, Mangaonkar AA, et al. Practical limitations of monocyte subset repartitioning by multiparametric flow cytometry in chronic myelomonocytic leukemia. Blood Cancer J. 2019;9(9):65.

  3. Otesteanu CF, Ugrinic M, Holzner G, Chang YT, Fassnacht C, Guenova E, et al. A weakly supervised deep learning approach for label-free imaging flow-cytometry-based blood diagnostics. Cell Rep Methods. 2021 Oct 25;1(6):100094. doi:10.1016/j.crmeth.2021.100094

  4. Ewings FM, Ford D, Walker AS, Carpenter J, Copas A. Optimal CD4 count for initiating HIV treatment: impact of CD4 observation frequency and grace periods, and performance of dynamic marginal structural models. Epidemiology. 2014;25(2):194-202. doi:10.1097/EDE.0000000000000043

By Elizabeth Boskey, PhD
Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases.